The present invention relates to a radio-wave transmitting cover arranged in a radio wave path of a radio-wave radar device and to a method for setting the thickness of the radio-wave transmitting cover.
Recent automobiles are equipped with a millimeter wave radar device (hereinafter, referred to as a radar device) for detecting the distances to surrounding automobiles and obstacles. Such a radar device is mounted on the back of the emblem on the front side or on the back of the front grille of an automobile (for example, Japanese Laid-Open Patent Publication No. 2016-80479). In this case, the emblem or the like functions as a radio-wave transmitting cover (hereinafter, referred to as a cover), through which the millimeter waves pass. Conventionally, to suppress the attenuation of the radio waves passing through the cover in order to improve the detection accuracy, the thickness of the cover is set in the following manner. That is, the thickness is made even and set to a value that is obtained by multiplying, by an integer, half of the wavelength of the radio wave of a radar device (the millimeter wave).
In such a conventional cover, the thickness is set to an even thickness as described above. This effectively reduces the attenuation of radio waves incident at an incident angle of 0° with respect to the cover when the radio waves pass through the cover. That is, the attenuation of the radio waves incident at a right angle with respect to the cover when passing through the cover is effectively reduced. However, when attempting to widen the angular range of detection of the radar device, the incident angle increases, and the attenuation of radio waves when passing through the cover increases. It is thus difficult to increase the detection accuracy of the radar device near the outer edge of the angular range of detection.